The present invention relates to rotorcraft and, more particularly, to reaction-drive rotorcraft having an adjustable rotor blade jet.
Referring to the drawings, FIG. 1 shows a rotor blade of conventional reaction-drive rotorcraft, generally designated by reference number 10. The blades 10 of reaction-drive rotorcraft are propelled by high-pressure gas exhausted from an orifice 12 positioned on a trailing edge 14 of the each blade. Reaction-driven rotor blades 10 include an outer skin 16 and internal structural components 18. The orifices 12 are openings in the outer skin 16 at the trailing edge 14 of the blade 10. The internal structural components 18 typically include a leading spar 20 located adjacent a leading edge 22 of the blade 10 and a trailing spar 24 located adjacent the trailing edge 14 of the blade. Because the orifice 12 is positioned at or very close to the trailing edge 14 of the blade 10, the trailing spar 24 can only extend continuously radially outward or outboard as far as the orifice 12.
Because the trailing spar 24 of conventional reaction-driven rotor blades 10 cannot extend continuously and uninterrupted outboard beyond the orifice 12, the orifice must be positioned sufficiently outboard so the trailing spar can extend radially outward enough to provide sufficient structural integrity for the blade. Many drawbacks relate to the limitations for orifice 12 positioning. A first drawback is a lack of design flexibility with respect to orifice 12 positioning. That is, the orifice 12 of conventional reaction-driven rotor blades 10 cannot be moved much farther inboard even when it is determined that moving it inboard would have many benefits because structural integrity of the blade would be compromised as a result of the shorter trailing spar 24. Another drawback of needing to have the orifice 12 far outboard is that ductwork 26 channeling the high-pressure gas to the orifice must extend farther, all the way along the blade to the orifice. This ductwork 26 extension requires additional material and increases weight. A further drawback is the blade 10 must be made thicker or otherwise larger adjacent a blade tip 28 to accommodate the orifice 12 and increased ductwork 26. The larger blade 10 adds weight, which is generally undesirable in blade design, especially farther outboard on the blade where centrifugal forces are higher during rotor operation.
The orifices 12 of conventional rotorcraft also have a constant opening 30 size. Thus, high-pressure gas passing to and through the rotor blade 10 of conventional rotorcraft will exhaust from the orifices 12 at a generally constant mass flow. Although constant mass flow is desirable at times during rotorcraft operation, the constant-sized orifices 12 do not allow changes to mass flow, which would be very beneficial at other times.